This is a dose escalation study of intravenous DX-8915f, a totally synthetic analogue of camptothecin which was synthesized to impart increased aqueous solubility, greater antitumor efficacy, and less toxicity than camptothecin itself, topotecan or irinotecan. The study will determine the maximum tolerated dose, the toxicity characteristics (including dose-limiting toxicity), the pharmacokinetic profile, the recommended dose for phase II studies, and the potential anti-tumor activity. The study drug has demonstrated, in vitro, more potent activity than camptothecin and topotecan against various types of human tumor cell lines including breast, lung, gastric, and colon cancer.